Adding public volume mounts for clone user.

Public SdCard Volumes are mounted only for user 0
(foreground user). This gives ENONT if the cloned
user tries to access the files in SdCard with
paths like "/storage/AB02-G212/DCIM/"

This change adds SdCard Volume mnt under
/mnt/usr/<cloned-user>/ which allows cloned apps
access to SdCard via direct file paths.

Bug: 203395175
Test: Manual by building and flashing device.
Change-Id: I091c40d3cb19915145cd5af40d1e79d5a9ecfa02